public interface DocCollectionWatcherCallback registered with
ZkStateReader.registerDocCollectionWatcher(String, DocCollectionWatcher)and called whenever the DocCollection changes.
boolean onStateChanged(DocCollection collection)Called when the collection we are registered against has a change of state.
Note that, due to the way Zookeeper watchers are implemented, a single call may be the result of several state changes. Also, multiple calls to this method can be made with the same state, ie. without any new updates.
collection- the new collection state (may be null if the collection has been deleted)
- true if the watcher should be removed